The present invention relates to a gas flow construction module, used in the gas handling system of a medical respiratory gas analyzer for the constriction, distribution and control of a flow.
In patient monitoring, the contents of respiratory gases are generally monitored by using a gas analyzer. In a so-called sidestream monitor, a sample of gas to be analyzed is passed from the respiratory tract of a patient or from respiratory tubes into a gas monitor for analysis. Since the gas often carries along some water, phlegm and dust, the sampling system must first of all be capable of separating some of these substances, which are highly detrimental to measuring sensors, and second of all, the device must be tolerant of these substances as possible without blocking.
Gas flow constriction is an essential part of both the sample flow control mechanism and the water separation system (see e.g. a water separation system disclosed in U.S. Pat. Nos. 4,382,806 and 4,304,578).
In addition to limiting the rate of gas flow, the flow constriction should exhibit several properties:
constriction must not be of such a "small hole size" that it is blocked due to dust particles. PA1 The constriction must tolerate temporary filling with water, e.g. during washing, disinfection or water separator overload. Water must also be readily removable from the constriction.
These requirements are often fulfilled by using a long, thin plastic tube. However, such tube-formed constriction has several drawbacks, including mechanical vulnerability, difficult installation, connections to other tubes of different thicknesses are difficult, and `slippery` plastics materials (e.g. teflon or polyethene) are not easily glued. A consequence of these drawbacks is poor productivity.